ZONE – The unit of division in State Plane Coordinate Systems created where state boundaries extend beyond limits imposed in the design of the projection system. Where the scale error between a geodetic distance and its grid representation exceeds 1 in 10,000 a state was usually divided into two or more zones. A new origin is used for each zone. See DANGER ZONE.
Zero - Zero degrees, minutes, and seconds. A perfect zero
Zenith is the direction pointing directly above a particular location